Tissue culture techniques are being successfully used in developing tissue and organ equivalents. The basis for these techniques involve collagen matrix structures, which are capable of being remodeled into functional tissue and organs by the right combination of living cells, nutrients, and culturing conditions. Tissue equivalents have been described extensively in many patents, including U.S. Pat. Nos. 4,485,096; 4,485,097; 4,539,716; 4,546,500; 4,604,346; and 4,837,379, all of which are incorporated herein by reference. One successful application of the tissue equivalent is the living skin equivalent, which has a morphology similar to actual human skin. The living skin equivalent is composed of two layers: the upper portion is made of differentiated and stratified human epidermal keratinocytes that cover a thicker, lower layer of human dermal fibroblasts in a collagen matrix. Bell, et al., "Recipes for Reconstituting Skin," J. of Biochemical Engineering, 113: 113-119 (1991).
Studies have been done on culturing corneal epithelial and endothelial cells. Xie, et al., "A simplified technique for the short-term tissue culture of rabbit corneal cells," In Vitro Cellular & Developmental Biology, 25: 20-22 (1989), and Simmons, et al., "Corneal Epithelial Wound Closure in Tissue Culture: An in vitro Model of Ocular Irritancy," Toxicology and Applied Pharmacology, 88: 13-23 (1987). Developing an in vitro organ equivalent of the cornea of the eye is of particular interest for use in in vitro toxicity assays to serve as accurate and inexpensive non-animal predictive models of in vivo ocular and dermal irritation potential for many types of products and raw materials.